Transformer oils



Patented as.

UNHTE TRANSFORMER OILS Earl Amott, Long Beach, Calif., assignor to Union Oil Company of California, Los Angeles, Calif., a corporation oi California No Drawing. Application January 2, 1942, Serial No. 425,451

4 Clalms.- (Cl. 252-64) This invention relates to mineral oils adapted for use as transformer oils and in connection with similar electrical equipment. The particular object of the invention is to produce a transformer oil having high resistance to oxidation even in the presence of copper.

Primarily the invention resides in a light mineral oil, such as is commonly used for electrical transformers, containing a very minor proportion in the order of a few tenths of one percent of a tartaric acid ester.

In practicing the invention, a considerable number of tartaric acid esters have been tested. These tests have included the tartaric acid esters of secondary alcohols and primary alcohols, including straight chain alcohols and branched chain and cyclic alcohols such as cyclo-hexyl and benzyl alcohols. The esters of the branched chain and cyclic alcohols constitute an important group especially the cyclo-hexyl, iso-propyl, iso-amyl and benzyl esters. Evidently, the cyclics may, for this purpose, be considered branched. Viewed from another standpoint, the esters of the secondary alcohols are very desirable, and perhaps preferable especially since the cyclo-hexyl and iso-propyl esters have proved so far to be respectively the best. The esters of the straight chain alcohols containing less than about ten carbon atoms are also quite desirable, especially the butyl esters. However, no tartaric acid esters have been tested which do not appear to be sufiiciently valuable to have some importance.

The invention extends to these groupings as indicated. Preferred individuals are di-cyclohexyl tartrate, di-iso-propyl tartrate, di-butyl tartrate, di-iso-amyl tartrate and di-benzyl tartrate in the order indicated.

In preparing transformer oils in accordance with this invention, a usual light mineral oil employed in electric transformers and well known to the industry has about 0.2% of the selected tartrate dissolved therein. This particular amount does not appear to be critical inasmuch as smaller proportions such as 0.05% yield an appreciable anti-oxidant eifect, and inasmuch as larger percentages afford equally good protection and possibly somewhat better protection in some instances, although it does not appear that any additional advantage is obtained when the percentage of ester is increased above about 0.5%.

The preparation of transformer oils according to this invention requires nothing more than the simple solution of the small percentage of the selected ester of tartaric acid in the oil.

Oils which have been made and tested containing specific esters are shown in the accompanying table. The first column of figures gives sludge and acid number and indicates results of what has been considered a very severe test. Here the oil was heated in the presence of copper for seven days at the distinctly elevated temperature of 120 C. These oils which showed sludge and. acid number of less than about 1.0 in this seven day test and did not show undue darkening, are considered especially valuable.

However, this test in the presence of copper eliminates a number of oils which will be adequate for commercial uses. For these purposes the less severe test shown in the second column of sludge and acid numbers was made on each 011. This test consisted of heating the same specimens at the same temperature of 120 C. for fortyfive days in the absence of copper, as distinguished from heating in the presence of copper for the seven day test. In this less severe test. the esters of secondary butyl alcohol, the octyl alcohol, and the higher carbon content lauryl and stearyl alcohols, which gave sludge or acid numbers approximating 1.0 or more in the severe test. showed good results in the less severe test. This indicates these materials to be good at least for ordinary commercial purposes. Even the unsaturated allyl alcohol ester is adequate. It was difiicult to obtain pure alcohols of the lauryl and stearyl types for test. It is likely that esters of the pure alcohols will rate higher.

Transformer oils heated at 120 centigrade in glass with indicated esters Copper present, Copper absent, heated 7 days heated 46 days Oilcontaining0.20%

oi tartaric dl-ester s} d Acid Sludge. Acid g? No. 1111.110 111]. No.

No additive 1.08 1.07 0.30 0.96. Secondary alcohols:

Cyclohexyl- 0. 45 0. 86 None 0.28. Isopropyl 0. 0.89 .do 0.47. Sec. amyl 0.83 0.95 Moderate im rovemcnt over base 0 Sec. butyl 1. 3; l. 38 None Less than 0.5. Primary alcohols Branched chain or cyclic- Benzyl 0. 31 0. 44 Improvement over base 0 Isoamyl..-.. 0. 65 0.83 None 0.13. Isobutyl. 0. 77 0. 71 Moderate improvement. 2-ethylyliexyl 0. 93 0. 87 Improvement.

0 Straight 0118211- Butyl 0.65 0. 78 None 0.29.

0. 75 0. 77 do Less than 0.5. 0.85 0.88 ..do Less than 0.5. 0. 88 0. Improvement. 0. 99 1. 02 0.4. 0.84. 1.75 1.48 Less than 0.5.

In the above table the sludge indication of milliliters of sludge per ten milliliters of oil is for color conversion. The only ones that might be considered obiectionably dark were the specimens containing the secondary butyl ester, the the standard ASTM precipitation number. Most of the materials tested produced at the most only very slight darkening in the oils in usual tests moms:

type and a small proportion, less than about 0.5%, sui'licient to inhibit oxidation or said transformer oil, of a tartaric di-acid ester of a cyclic alcohol.

2. A transformer oil consisting essentially 'of a light mineral oil of the transformer oil type and a small proportion, less than about 0.5%, sumcient to inhibit oxidation of said transformer oil, of di-cyclo-hexyl tartrate.

3. A transformer oil consisting essentially or a light mineral oil of the transformer oil type and a small proportion, less than about 0.5%, of a tartaric acid este of a saturated cyclic alcohol.

4. A transformer 011 according to claim 3 sub- 15 stantially free from corrosive soaps.

EARL AMO'I'I'.

Certificate of Correction Patent N 0. 2,397,332.

EARL AMOTT It 1s hereby certified that error appears in the March 26, 1946.

printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line 1 begin rung with the words for color strike out all to and includin 1n hne 6 after tests read with this correction therein that the s and insert the same in the Patent Office.

; and that the said g ester, the in line 3, Letters Patent should be ame may conform to the record of the case Signed and sealed this 10th day of September, A. D. 1946.

LES LIE FRAZER,

First Assistant Oommz'ssz'oner of Patents. 

